ds--,
Is this the Grayscale Bitcoin Trust you are talking about? If so you should take a look at
https://grayscale.com/wp-content/uploads/2023/01/Grayscale-BTC-Annual-Reporting-12.31.22-Final.pdf
to see how they calculate the 1099-B they sent. It may well be that you multiple by 115 in the end.
On the bigger picture side, when adjustments to cost basis reduce the cost basis to zero and below, which is most frequently seen with return of capital by real estate and utility companies. the cost basis remains zero, but you are subject to capital gains taxes on the amount that would have been below zero. If the investment was the bitcoin one, the reported loss on the 1099B would need to be split into the loss that drove your investment basis to zero and the rest of the loss turned into an adjustment that reduced the total loss. Whew.
